Poland syndrome (PS) has been described as unilateral pectoral muscle deficiency variably associated with ipsilateral thoracic and upper limb anomalies. Bilateral hypoplasia/aplasia of the pectoralis muscle and upper limb defects in association with variable thoracic muscles, chest wall deformities and lower limb defects have been infrequently reported in the literature. We report on a 3½-year-old girl with clinical features consisting in bilateral asymmetric pectoral muscle defects (complete agenesis on the left side and agenesis of the sternocostal head on the right side), nipple hypoplasia, left rib defect, and right hand symbrachydactyly. In this study, we reviewed the bilateral features present in our patient and those described in the literature. Hypotheses explaining bilateral features in PS are reviewed. © 2009 Wiley-Liss, Inc.